Maximum safe load indicators for cranes



Dec. 12, 1967 H. BOUGHTON 3,357,571

MAXIMUM SAFE LOAD INDICATORS FOR CRANES Filed Jan. 18, 1966 3 Sheets-Sheet 1 12, 1967 J. H. BOUGHTON 3,357,571

MAXIMUM SAFE LOAD INDICATORS FOR CRANE Filed Jan. 18, 1966 I 5 Sheets-Sheet 2 Dec. 12, 1967 J. H. BOUGHTON MAXIMUM SAFE LOAD INDICATORS FOR CRANES 5 Sheets-Sheet 5 Filed Jan. 18, 1966 vat United States Patent 3,357,571 MAXIMUM SAFE LOAD INDICATORS FOR CRANES John H. Boughton, Amersham Common, England, assignor to T. T. Boughton & Sons Limited, Amersharn, Buckinghamshire, England, a British company Filed Jan. 18, 1966, Ser. No. 521,327 5 Claims. (Cl. 21239) ABSTRACT OF THE DISCLOSURE A side jib mobile crane has a superstructure mounted on its chassis for limited angular upward movement relative thereto about an axis extending along one side of the chassis in response to the upsetting couple caused by loading, superposed flanges extend from the other side of the chassis and superstructure and are secured together by bolted connections incorporating resiliently yieldable washer plates to permit movement of the superstructure flange away from the chassis flange only when the upsetting couple exceeds a predetermined value, and a switch is operated by such relative movement of the flanges to actuate a warning signal or the like.

This invention relates to side boom mobile cranes, by which is meant for the purposes of this specification mobile cranes having a derricking jib at one side of the crane, the axis of derricking (luiiing) movement of the jib being parallel to the direction of length of the crane. The crane may be either a tractor-mounted crane or a tractordrawn crane.

The invention has for its object to provide a novel construction for side boom cranes embodying improved means for indicating when the load being lifted by the crane is approaching, has reached or is in excess of the maximum safe load.

It is well known that the safe load for any particular jib crane varies with the radius at which the load is being raised. Thus loads which are safe when the jib of the crane is near the vertical will become increasingly dangerous as the jib is moved towards a horizontal position.

In the past it has been normal practice, when a safe load indicator has been required on a jibcrane, to operate the indicator by measuring the tension in either the hoist rope or the derricking rope. The measurement given in this case is a measurement of the load being lifted and this measurement has to be compensated in accordance with the radius at which the load is being lifted before it can be used to operate a safe load indicator. Such compensation has normally been performed by means of a cam arrangement for which the cam has to be cut specially for each individual crane. This system is therefore expensive and it suffers from a number of disadvantages. Firstly, the cam must be changed if the length of the jib of the crane is altered. Secondly, if the tension measuring device is located in the derrick rope, the cam must be changed if the mechanical advantage of the derricking system is altered.

According to the present invention there is provided a side boom mobile crane comprising a chassis; a superstructure thereon mounting at least the hoisting mechanism of the crane, said superstructure being so mounted on the chassis as to possess freedom for limited angular movement relative thereto about a horizontal axis fixed in the chassis and disposed parallel to the direction of length of the chassis whenever the upsetting couple acting on the crane (by which is meant, here and throughout this specification and the appended claims, the resultant turning moment about said horizontal axis, produced by all of the forces acting on the superstructure and on the ice parts mounted thereon when the crane is lifting a load) reaches a predetermined value representing a condition of loading of the crane approaching, coinciding with or exceeding the maximum safe loading condition for which the crane has been designed; control means operative in response to the occurrence of said angular movement; and means operable under the control of said control means to give a Warning signal to the operator of the crane of the existence of said condition of loading and/ or stop or initiate stoppage of the hoisting gear of the crane.

According to a generally preferred construction, the jib is pivoted to the chassis frame.

Further according to a generally preferred construction, the control means are located at a position remote from said horizontal axis. In the particular embodiment of the invention hereinafter described the horizontal axis aforesaid is located at the side of the crane at which the jib is located and the control means are located at the opposite side of the crane. This, generally speaking, is the most advantageous arrangement.

The construction may conveniently be one wherein the angular movement of the superstructure is performed against the constraint of resilient means operative to prevent the movement until such time as the upsetting couple commences to exceed said predetermined value.

In such case, and in the event of the construction being one in which the horizontal axis aforesaid is located at the side of the crane at which the jib is located and the control means are located at the opposite side of the crane, the arrangement may be one wherein at said opposite side of the crane the superstructure is bolted to the chassis frame by means of a bolted connection which is designed to yield to the upward pull of the superstructure, with resulting angular movement of the latter about said horizontal axis and consequent operation of the warning signal means or hoisting mechanism control means, whenever the upsetting couple commences to exceed said predetermined value.

Said bolted connection may comprise at least one bolt associated with a resilient member against which the bolt is tightened to make the connection, said resilient member being adapted to yield to said upward pull of the superstructure whenever the upsetting couple commences to exceed said predetermined value.

In this event, a convenient construction is one wherein said resilient member is constituted by a plate having an opening in it through which the shank of the bolt extends and on the face of the plate which is towards the parts which are bolted together by the connection, a recess bounded by the opening as regards the inner periphery of the recess and serving to render the plate yielding to said upward pull of the superstructure, and wherein the bolted connection comprises also a second plate interposed in the connection between the first plate and said parts that are bolted together by the connection, said second plate also having an opening in it through which the shank of the bolt extends and on the face of the plate which is directed towards the first plate a recess registering with the recess in the first plate, the arrangement be ing such that the extent of freedom for yielding movement of the first plate is determined by the combined depth of the two recesses in the plates.

The arrangement may be one in which the signal means gives at least two successive signals corresponding respectively to successively increasing conditions of loading.

The warning signal means, or the hoisting mechanism control means, may be electrically operated through the agency of switching means, e.g. a microswitch, said switching means constituting said control means operative in response to the occurrence of the angular movemen of the superstructure. v y

The invention will now be further described with reference to the accompanying drawings, which illustrate one embodiment by way of example, the crane inthis embodiment being a tractor-mounted crane.

In the drawing:

FIGURE 1 is an end view of the crane;

FIGURE 2 is a side elevation of the crane, looking in the direction of the arrow a in FIGURE 1;

FIGURE 3 is a fragmentary elevational view of the crane, again looking in the direction of the arrow a and drawn on a larger scale than FIGURE 2, the view showing details of the yieldable bolted connection hereinbefore described as between the chassis frame of the crane and the superstructure thereof, also, in ,a purely schematic manner, the microswitches which control the warning signal means in dependence on the value of the upsetting couple acting on the crane;

3 FIGURE 4 is a corresponding plan view to FIGURE FIGURE 5 is a fragmentary sectional view, on the section line 55 of FIGURE, illustrating said bolted connection in greater detail, the view being drawn on a larger scale than FIGURES 3 and 4.

Like reference numerals are used to denote like parts in the various figures.

The crane shown comprises a Caterpillar or endless tracked tractor chassis generally indicated at A and a superstructure thereon generally indicated at B, the superstructure, which mounts the hoisting mechanism of the crane, of which hoisting mechanism elements are shown more or less diagrammatically at 3 and 4, being mounted on the frame of the chassis in the particular manner later described.

The chassis frame, two portions of which, at the two lateral extremities of the frame, are shown in FIGURE,

1 at 5 and 6 respectively, carries, at the left-hand side of the frame in FIGURE 1, the pivot 7 of the crane jib 8.

superstructure B over-spans the chassis frame and includes two wing portions 9 and 10 which extend respectively along the two sides of the structure and carry respectively two horizontal flanges 11 and 12.

Portions 5 and 6 of the chassis frame carry respectively two horizontal flanges 13 and 14 which underlie and abut flanges 11, 12.

At the left-hand side (in FIGURE 1) of the crane the superstructure is hinged or fulcrummed to the chassis frame so as to be angularly movable relative thereto about an axis extending lengthwise of the crane and located in the plane of the joint between in two flanges 11, 13.

At the opposite (right-hand in FIGURE 1) side of the crane the superstructure is bolted to the chassis by two strong identical bolts 15 and 16 located respectively at two positions spaced apart from one another lengthwise of the crane.

Thesebolts are accommodated in vertical bosses 17, 18 welded to side portion 6 of the chassis frame, to flange 14 of the chassis frame and in the case of each boss to an abutment plate 19 or 20 located at the bottom of the boss.

Each bolt consists of a shank position s (FIGURE 5) and a head portion 21 formed integrally with the shank portion. Shank portion s extends through a hole 22 in flange 12,, a hole 23 registering with hole 22 in flange 14, a bore 24 registering with holes 22 and 23 in boss 17 or 18 and a hole registering with bore 24 in abutment plate 19 or 20. Beyond the abutment plate 19 or 20 the shank portion s extends through the central openings 25, 26 of two identical washer plates 27, 28 formed in each case, on the face of the plate directed towards the face of the opposite plate, with an annular recess 29 or 30 extending, radially of the plate, from the inner periphery f the central opening therein so as to leave a relatively narrow annular land formed by a marginal portion of the recessed face of the plate. The two plates 29, 36 are firmly clamped against the lower face of the relative abutment plate 19 or 20, by a nut 31 screwed on to a threaded end portion 32 of the shank portion of the corresponding bolt 15 or 16.

As already stated, superstructure B is pivotally connected to, or fulcrummed on, chassis A at the left-hand side of the crane so as to possess freedom for upward angular movement relative thereto. It is normally prevented from such movement, however, by the bolts 15, 16, which operate to hold the two flanges 12 and 14 and therewith the two flanges 11 and 13 at the left-hand side of the crane in firm engagement with one another, until such time as the upsetting couple acting on the crane commences to exceed the predetermined value hereinbefore referred to, when the tension obtaining in ho.ts 15, 16, exercised through nuts 31, flexes the washer plates 28 inwardly (i.e. in the direction toward the washer plates 27) against their inherent resilience, so permitting flange 12 of the superstructure to rise slightly relative to flange 14 of the chassis frame-the superstructure performing in consequence a corresponding measure of angular movement relative to the chassis frame under the pull of the load hanging on the jib of the crane.

Such angular movement of the superstructure occasions actuation of a microswitch 32 with resulting operation of a warning signal means (not shown), which can be arranged to give either an audible signal or a visual signal, or both, signifying to the operator of the crane that the load beinglifted is approaching, or has reached, or is in excess of the maximum safe load for which the crane has been designed, the microswitch being mounted on flange 12 of the superstructure and being normally held in non-actuated (circuit-open) condition by a set screw 33 finely adjustable along a tapped hole provided to receive it in flange 14 of the chassis frame.

If desired, there may be a series of two or, more microswitches bringable into actuated condition in succession as the load on the jib increases from a value approaching the maximum safe load to a value equal thereto or to a value in excess of the maximum safe loadaccording to the requirements of the indicator system. In the arrangement shown threre are two such successively actuatable microswitches, namely the one marked 32 and a second one marked 34.

In the event of the control means aforesaid, operable in response to the angular movement of the superstructure, being used to stop or initiate stoppagev of the hoisting gear of the cranes in the manner hereinbefore visualised, said control means may be constituted, for example, by a microswitch similar to the microswitches 32, 34, and the hoisting gear control means itself may take any convenient form.

Various modifications are possible. For example, the signal means or as the case may be, the means for stopping or initiating stoppage of the hoisting gear, may be pneumatically or hydraulically operated instead of being operated electrically. Also the bolted connection, yieldable to excessive upsetting couple forces, between the superstructure and the chassis of the crane, may take any other form than that described with reference to the drawings. All such modifications are to be understood as within the scope of the invention as defined by the claims.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A side jib mobile crane comprising a chassis, a superstructure overspanning said chassis, means at one side of said chassis and superstructure mounting the latter on the chassis and permitting angular upward movement of said superstructure relative to said chassis about a horizontal axis extending along said one side thereof, hoisting mechanism mounted on said superstructure so that loading of the crane results in an upsetting couple tending to cause angular upward movement of said superstructure relative to said chassis about said axis, a first flange on the other side of said chassis, a second flange on the other side of the superstructure overlying said first flange, said first and second flanges having registering holes therein, a plurality of bolts extending through said registering holes in said flanges, a pair of resiliently yieldable washer plates held on each bolt by a respective nut so that said bolts, washer plates and nuts force said first and second flanges together and resist movement of said second flange away from said first flange until said upsetting couple exceeds a predetermined value to cause flexing of said washer plates, and switch means operated by movement of said second flange away from said first flange.

2. A side jib mobile crane comprising a chassis, a superstructure mounted on the chassis frame so as to possess freedom for limited angular movement relative thereto about a horizontal axis disposed at one side of the chassis frame and parallel to the lengthwise direction thereof, a jib pivoted to said one side of the chassis frame, hoisting mechanism mounted on the superstructure, cooperating flanges on said superstructure and said chassis frame at the sides thereof opposed to the side of the chassis frame on which the jib is pivoted, a plurality of bolts passing through said flanges to constitute connections therebetween, each bolt having thereon at least one resilient member adapted to yield to an upward pull of the superstructure whenever the upsetting couple acting on the crane reaches a predetermined value, control means operative in response to upward movement of the flange on the superstructure relative to the flange on the chassis frame and warning means operative in response to operation of said control means.

3. A crane as claimed in claim 2, wherein said resilient member is constituted by a plate having an opening in it through which the shank of the bolt extends, and wherein there is a recess in the face of the plate which is towards the parts which are bolted together by the connection, said recess being bounded by the opening as regards the inner periphery of the recess and serving to render the plate yielding to said upward pull of the superstructure.

4. A crane as claimed in claim 3, wherein said plate is circular, the opening in the plate is also circular and is concentric with the plate, and the recess is of annular formation and is also concentric with the plate.

5. A crane as claimed in claim 4, wherein each bolt connection comprises also a second plate interposed in the connection between the first plate and said parts that are secured together by the connection, said second plate also having an opening in it through which the shank of the bolt extends and on the face of the plate which is directed towards the first plate a recess registering with the recess in the first plate, the arrangement being such that the extent of freedom for yielding movement of the first plate is determined by the combined depth of the two recesses in the plates.

References Cited UNITED STATES PATENTS 2,858,070 10/1958 Scharff 212-39 2,910,189 10/1959 Scheuerpflug 212-39 3,223,249 12/1965 Cady 212-39 3,265,218 8/1966 Stefanutti 212-8 ANDRES H. NIELSEN, Primary Examiner. 

1. A SIDE JIB MOBILE CRANE COMPRISING A CHASSIS, A SUPERSTRUCTURE OVERSPANNING SAID CHASSIS, MEANS AT ONE SIDE OF SAID CLASSIS AND SUPERSTRUCTURE MOUNTING THE LATTER ON THE CHASSIS AND PERMITTING ANGULAR UPWARD MOVEMENT OF SAID SUPERSTRUCTURE RELATIVE TO SAID CHASSIS ABOUT A HORIZONTAL AXIS EXTENDING ALONG SAID ONE SIDE THEREOF, HOISTING MECHANISM MOUNTED ON SAID SUPERSTRUCTURE SO THAT LOADING OF THE CRANE RESULTS IN AN UPSETTING COUPLE TENDING TO CAUSE ANGULAR UPWARD MOVEMENT OF SAID SUPERSTRUCTURE RELATIVE TO SAID CHASSIS ABOUT SAID AXIS, A FIRST FLANGE ON THE OTHER SIDE OF SAID CHASSIS, A SECOND FLANGE ON THE OTHER SIDE OF THE SUPERSTRUCTURE OVERLYING SAID FIRST FLANGE, SAID FIRST AND SECOND FLANGES HAVING REGISTERING HOLESS THEREIN, A PLURALITY OF BOLTS EXTENDING THROUGH SAID REGISTERING HOLES IN SAID FLANGES, A PAIR OF RESILIENTLY YIELDABLE WASHER PLATES HELD ON EACH BOLT BY A RESPECTIVE NUT SO THAT SAID BOLTS, WASHER PLATES AND NUTS FORCE SAID FRIST AND SECOND FLANGES TOGETHER AND RESIST MOVEMENT OF SAID SECOND FLANGE AWAY FROM SAID FIRST FLANGE UNTIL SAID UPSETTING COUPLE EXCEEDS A PREDETERMINED VALUE TO CAUSE FLEXING OF SAID WASHER PLATES, AND SWITCH MEANS OPERATED BY MOVEMENT OF SAID SECOND FLANGE AWAY FROM SAID FIRST FLANGE. 